Fluid-tight packing for floating-rooftype hydrocarbon tanks



M. MERCIER 3,054,526

FLUID-TIGHT PACKING FOR FLOATING-RooF-TYPE HYDRocARBoN TANKS Sept. 18, 1962 Filed April 22, 1960 Patented Sept. 18, 1962 3,054,526 FLUID-TIGHT PACKING FR FLOATING-ROOF- TYPE HYBROCARBN TANKS Maurice Mercier, 172 lnulevard du Montparnasse, Paris, France Filed Apr. 22, 1969, Ser. No. 24,158 Claims priority, application France Apr. 25, 1959 2 Claims. (Cl. 22d- 26) Y the stored liquid is 4screened from all contact with the open atmosphere.

Packings resorted to hitherto consist either of metal scrapers which are applied by mechanical means against the fixed Wall of the tank and are connected to the pontoon by resilient membranes, or of rubber packers of generally tubular shape which are applied both against the periphery of the pontoon and the inside of the wall by the resilient pressure exerted by a gaseous or liquid uid.

In addition to this principal sealing device, floating roofs resorted to hitherto comprise a secondary seal the purpose of which is to prevent rainwater from penetrating into the product under storage.

The present invention has for its object a iluid-tight packing system in which an annular plastic membrane, shaped like a deep gutter, is applied against the side of the tank under the pressure exerted by a dense, spheroidal and granular ller material; furthermore, the shape of the gutter enables it to collect and drain away rainwater.

The advantage of the invention resides in the small membrane area which enters into its desigi, in the relative invulnerability of this membrane, the solid iiller material of which cannot empty through a small hole as would be the case if a liquid iiller were used, and, lastly, in the dual sealing role of this membrane with respect to the liquid and the stored gas on the one hand and the rainwater on the other.

The invention will be clearly understood from the following description given with reference to the accompanying drawings ywhich illustrate, by Way of example only and not in a limiting sense, various possible embodiments of the devices designed to allow the principles referred to hereinabove to be put into application.

In these drawings,

FIG. 1 is a sectional view of a fluid-tight device according to the invention.

FIG. 2 is a detail view of the method of assembling the membrane to its hoop.

FIG. 3 is a variant, in which the fluid-tight device is mounted on a pontoon having an inclined generating line.

FIG. 4 is a variant of a suspension device for the free rim of the membrane.

Referring now to the drawings, it will be seen that FIG. l is a partial section View in elevation of the tank, the pontoon and the fluid-tight packing. In this iigure, the

wall of the tank is designated by the numeral 1, the bottom and top of the iloat by the numerals 2 and 3 respectively, the level of the liquid by the numerals 4 and 4 and the vertical wall of the iioat by the numeral 5.

The fluid-tight packing consists of a membrane 6 manufactured out of a molded sheet of rubber or plastic material. This membrane is fixed rigidly and in sealing fashion to the wall 5 of the float by means of bolts 7 which pass through notches 8 in a flange 9 welded in hermetic fashion to the wall 5.

The free rim of the membrane is rendered rigid by a flat iron hoop 10 to which it is bolted. This flat hoop is of generally circular shape and may be expandable or non-expandable. The iron hoop and the membrane which it reinforces are supported by means of inclined connecting rods ll-say one or two in number per yard of tank circumference-which are articulated at 12 and 13 respectively onto the hoop 10 and the wall 5 of the iloat. In consequence, the circular outer wall of the gutter-shaped membrane 6 can be pressed against the side 1 by the horizontal reaction generated by the rods 11 under the eiect of the gutters weight characteristic and the friction forces set up between the membrane and .the side.

The circular trough formed by the membrane is lled with a mass of dense and granular material 14 possessing as low internal cohesion characteristics as possible.

It will be appreciated that, similarly to the law governing the thrusting action of earth banked up against a vertical Wall, this mass of material will press the membrane against the Wall 1 and, through the medium of the rods 11, the weight of this iller material will produce a reaction that will apply the upper rim of the membrane against the wall 1.

A bearing and supporting surface 15, which may be either ilat and horizontal, or inclined, and which is integral with the wall 5, can be provided, if required, in order to insure improved application of the membrane 6 against the Wall 1.

It will thus be appreciated that these Various component elements together constitute a resilient fluid-tight packing which is integral with the float and which is pressed against the wall of the tank by the sideways thrust result-ing from the falling-in action of the granular material inside the gutter and by the horizontal reaction lset up by the rods against the upper hoop, both of which will vary with the weight of the granular material.

With this device, the force with which the membrane is pressed against the wall is Virtually independent of movement of the oat 2, 3, 5 with respect to the side 1 of the tank; moreover, such movement is authorized by the device without the fluid-tightness being aected.

The wall 1 is liable to accumulate rainwater, and this water which streams down the inner surface of 1 will be stopped 4by the rigorous manner in which the membrane 6 is applied against the wall 1 so that the rainwater spills into the gutter-shaped membrane, passing through the granular iiller material in the process. This rainwater collects at the bottom of the gutter and drains away via orices 16 into which debouch drainpipes 17 which evacuate the water out of the metal pontoon, the Water being thus drained away out of the tank in a manner well-known per se.

The connection effected between the pipes 17 of the easy to replace.

Vmetallic floating roof and this envelope or Wall. .danger is Very great if the membrane joining the metal illustrated by way of example only and that their exact positions will be determined according to the pressure which is required to be exerted by the membrane against the Wall of the tank, the acceptable amount of residual water to be left over Vin the gutter and the requirements in respect of ease of access to and servicing of the various parts of the system.

FIG. 2 shows the method of xing the top outer edge of the gutter-shaped membrane v6 to the hoop 10. This fixing is -achieved by means of bolts 18 having large button heads 19 which Ystand proud of the rubbing face 2G of the membrane to the extent of about one or two millimeters. This optional arrangement provides a means of protecting the edge of the membrane against undue friction leading to wear.l

FIG. 3 is a highly diagrammatic illustration of an embodiment of a duid-tight packer which is in every way identical to that in FIG. l except that the peripheralV wall of the pontoon is of truncated-cone shape to permit better utilization of the kgranular ller Vmaterial and to facilitate inspection and possible repairing of the membrane and its xing members.

Moreover, by reason of its conical shape, the -wall 5 embodies, at its bottom, a limiter of eccentricity with respect to the wall 1 of the tank. Y I

FIG. 4 represents an embodiment in which the rods Work in tension instead of in compression. The membrane, its rim flange, its fixing method and its -filler'material are identical to Vthose in FIG. l, but'the rods 21,

which-are articulated at `22 and 23, respectively, onto they hoop 25 and onto brackets 24, connect Vthe latter to the hoop 25 and operate in tension. The relative positionsof the articulations 22 and 23 and the hoop 25 enable horizontal thrusts to be set up which act upon the latter in the requisite direction and with the required force, in accordance with the intended purpose.

In the fluid-tight packing executed according to FIGS. 1, 3 and 4, the gutter-shaped membrane can be constituted either in a single piece surrounding the Ywhole of the' pontoon or in a multiplicity of individual elements each of which corresponds to a section only of the circumference, these several elementsbeing interconnected by means of fluid-tight seals and being interchangeable and Clearly, the greatest hazard to be feared in thek case of a tank containing hydrocarbons is fire.

In the case under consideration, such danger could arise Ithrough leaks occurring between the envelope or wall of the tank and the packing whichis applied between the Such iloat to the envelope cornes to be destroyed by tire, since the flames can then spread to the annular space comprised between the metallic floating roof and the envelope of the tank.

Such a re over a limited area can be successfully extinguished by producing at, or leading up to, the required Vspot a gas whichis incapable of sustaining combustion (examples being carbon' or sulphur anhydrides, nitrogen, etc.), in a quantity such that the inflammable hydrocar- Vbon vapors are prevented from coming into contact with the air and its oxidizing properties. Moreover, it is well known that air ceases to be an oxidizer when mixed with Y25% of inert gases.

According to the invention, Vthe production of such gases is automatically insured in the event of lire breaking out in the tank by a decomposition of the material in the gutter, for, as is well known,certain caribonates and 4 other metal salts give 0E inert gases at relatively low temperatures, namely gases which are incapable of sustaining combustion.

By way of a non-limiting example of such a carbonate may be cited zinc carbonate CO3 Zn which decomposes at 140 C. into carbon anhydride CO2 and zinc oxide ZnO, this being a product to 'be used in preference to others of a similar nature such as:

Basic carbonate of Pb:

Decomposition temperature: 180 C. Carbonate of cadmium:

CdCO3 Decomposition temperature: 357 C. Basic carbonate of copper Decomposition temperature: 200 C.

In the natural'state, carbonate of copper is known as Malachite and carbonate of zinc as Smithsonite- The above-mentioned carbonates can be utilized either in the form of small balls produced by breakage and subsequent abrasion in accordance with methods well-known Vper se, or in the for-m of balls molded by the addition of a lbinding agent consisting of live to fifteen percent of some thermoplastic material Vsuch as Vinyl chloride or polystyrene, or of some heat-hardenable material such as ureaformaldehyde or formol-formaldehyde resin.

Thus it will be appreciated that, if a certain quantity of metal salts in theform of spheroidal elements is placed inside a oating-roofs fluid-tight packing the membrane Vof which -is sufficiently refractory thanks to its reinforcing Wire mesh or to the incorporation ofV non-burning ma- VKterials, a large quantity of inert gas will be given off,

namely of gas incapable of. sustaining combustion, and

`that moreover the gas will be given oi precisely at the spot Where the outbreak of fire occurs. Y

By way of example only and not in a limiting sense, it will be indicated that if the seal of a tank measuring twenty meters in diameter be lled with carbonate of zinc, it is capable of giving ofl a two-meter-thick blanket of CO2 by total decomposition within the free space of the reservoir.

Since this gas is emitted precisely at the seat of the re,

Vit is extremely effective.

yand comprisingjn combination, a plurality of arms each hingedly connected at one end thereof to said roof and extending from said attached end toward the peripheral wallof said tank;V

a substantially rigid annular means hingedly attached to the other ends of said arms to be carried thereby; an annular membrane formed from fluid tight, ilexible and resiliently stretchable material fluid tightly attached along the outer edge thereof to said annular means and at the inner edge thereof to the peripheralwall of said roof at an elevationlower than the elevation of said annular Ymeans, the width of said membrane being greater than the distance between the attached edges thereof so that said mem- V:brane Vextends downwardly from said annular means along the peripheral wall of said tank across the space between the peripheral Walls to form with the peripheral wall of the roof an annular trough having a bottom portion below the attached inner edge of said membrane; Y Y

granular weighting material filling said trough substantially up to the elevation of said annular means so that the portion of said resiliently stretchable membrane extending downwardly from said annular means along the peripheral wall of the tank is radially outwardly expanded in tight engagement with said 6 ripheral wall of said tank across the space between the peripheral walls to form with the peripheral wall of the roof an annular trough having a bottom por- -tion below the attached inner edge of said membrane;

peripheral wall of said tank to form a fluid tight 5 and granular weighting material filling said trough seal thereagainst; and drain means communicating substantially up to the elevation of said annular with the interior of said annular trough in the region means so that the portion of said resiliently stretchof the bottom portion thereof for draining rainwater able membrane extending downwardly from said anentering said trough from the interior of the same. nular means along the peripheral wall of the tank is 2. A fluid tight seal between a peripheral wall of a 10 radially outwardly expandedintight engagement with tank and a Peripheral Wall 0f a floating IOO 0f the tank `said peripheral wal-l of said tank to form a tiuicl tight aI 1d Comprising, ill Combination, a plurality 0f 31H15 each seal thereagainst, said granular weighting material hmgedly connected at one end thereof to said roof and being formed from material adapted to emit a greextending .from said attached end toward the peripheral extinguishing gas at elevated temperatures. wall of said tank;

a substantially rigid annular means hingedly attached to the other ends of said arms to be carried thereby; References Clted m the me of thls patent an annular membrane formed from Huid tight, i'lex- UNITED STATES PATENTS ible and resiliently stretchable material fluid tightly attached along the outer edge thereof to said annular 1426997 Leland et al Aug' 22 1922 means and at the inner edge thereof to the peripheral 1463268 HUE July 31 1923 wall of said roof at an elevation lower than the ele- 1,931,551 Larson Oot- 24: 1933 vation of said annular means, the width of said mem- 1,994,477 Kramer Maf 19, 1935 :brane being greater than the distance between the 2,516,101 Bobe July 25, 1950 attached edges thereof so that said membrane extends 215311424 Goldsby et al NOV- 28, 1950 downwardly from said annular means along the pe- 2,968,420 Harris et al. I an. 17, 1961 

